1. Field of the Invention
The present invention relates to multilayer ceramic electronic components and methods for making the multilayer ceramic electronic components. In particular, the present invention relates to the structure of an external terminal electrode of a multilayer ceramic electronic component and a method for forming the external terminal electrode.
2. Description of the Related Art
In recent years, markets for small portable electronic appliances such as cellular phones, laptop computers, digital cameras, digital audio devices, etc., have expanded. These portable electronic appliances are achieving not only size reduction but also higher performance. Since a large number of multilayer ceramic electronic components are mounted on portable electronic appliances, multilayer ceramic electronic components are also required to achieve size reduction and higher performance. For example, multilayer ceramic capacitors are required to achieve size reduction and a higher capacitance.
In order to reduce the size of multilayer ceramic capacitors and increase their capacitance, it is effective to reduce the thickness of ceramic layers. Recently, capacitors having ceramic layers with a thickness of about 3 μm or less have been used in practical applications. Although further thickness reduction is currently being pursued, a problem arises in that short-circuits between internal conductors are more likely to occur with the thickness reduction of ceramic layers, thereby making it difficult to ensure the quality of the capacitors.
Another effective way is to increase the effective areas of internal conductors. However, for mass production of multilayer ceramic capacitors, side margins between the internal conductors and the side surfaces of the ceramic bodies and end margins between the internal conductors and the end surfaces of the ceramic bodies must be maintained in order to compensate for misalignment of stacked ceramic green sheets and cutting deviations. Thus, the amount by which the effective areas of the internal conductors can be increased is limited.
In order to increase the effective areas of internal conductors while maintaining sufficient margins, the areas of the ceramic layers must be increased. However, the amount by which the areas of the ceramic layers can be increased is limited due to designated size standards. Furthermore, the thickness of the external terminal electrodes is also a limiting factor.
Typically, external terminal electrodes of multilayer ceramic capacitors are formed by baking conductive paste that is applied on end portions of ceramic bodies. A common method for applying the conductive paste is to dip end portions of ceramic bodies in conductive paste disposed in a paste vessel. According to this method, the thickness of the conductive paste applied at the center portion of each end surface of the ceramic bodies tends to be greater than that of other portions due to the viscosity of the conductive paste. Thus, because the external terminal electrodes have thick portions (e.g., portions having a thickness exceeding about 30 μm), the areas of the ceramic layers must be decreased.
To overcome such a problem, a method for forming external terminal electrodes directly by plating has been proposed (e.g., see International Publication No. 2007/049456). According to this method, plating films are deposited on exposed portions (nuclei) of internal conductors exposed at end surfaces of ceramic bodies, and the exposed portions of adjacent internal conductors become connected to each other as the plating films grow. Thin, flat electrode films can be formed with this method as compared to the existing method that uses conductive paste.
However, according to this plating method, the glass-bonding effect that is achieved by the existing method using the conductive paste is not obtained. Thus, the bonding force of the plating films, e.g., external terminal electrodes, to the ceramic bodies is relatively weak.